Telephone ringing system



nc. 26, 1939. MPBE R 2,184,907

TELEPHONE RINGING SYSTEM Filed July 1, 1938 /mmw 1 1 75 .1 T l M P 8 Zia. 2

INVE-NTOR Jiwmes Cana vbzjlcfir BY ATTORNEY Patented Dec. 26, 1939 UNITED STAT.

TELEPHONE RINGING SYSTEM Jamesflampbell, Jr., Upper Darby, Pa, assignor to American Telephone and Telegraph Company, a corporation of New York I Application; July 1, 1838, Serial No. 217,055

Claims.-

This invention relates to electrical circuits and; more particularlyto-that class of circuits usedfor. selectiveringingor-signaling wherebya signal may be transmitted-to one or moreof a plu 5 rality. oflstations connected-to the same-line."-

In signalingv systems-proposed heretofore, each ringer circuit J. connected-'- tothe line might in cludea three-electrodegasefilled tube-comprisingfltwo cold cathodes and ananode, the -twocathodes:beingconnected across the line through a-large resistor, the resistor being-connected between one side of the line and one 'of -thetwo cathodes, the ringer itself being-connected .be-

tweeuthelanode and ground- A-similar ringercircuit might also be. connected in reversed-relation across the same line; that is, theresistorbeing connected between the other side of the line and one-of the cathodes. For such systems it .has been proposed to transmit ringing current in the form of an alternating current of a frequency, for eXamp-le,. of .twenty cycles superimposed upon a direct current.

It has been found, however, that such ringing circuitsare'falsely' operated by interfering currents which are induced 'orotherwiseimpressed' upon the line from foreign circuits such as electrified railroadsi- In other words;- the currents so-- induced into the line -have'"been 'found 'to operate-the ringers evenwhenno ringing current wastransmitted to those ringers. Such false operation-has, of -cours'e;'been objectionable.

It is 1 one u of-- the objects 0f :this invention to provide-a ringingcircuit employing gas-filled tubes which will not operate when interfering "currents of the type referred to become superimposed. on the line, butwill respond only to ringing currents alone.

Another of the objects of this invention is to provide a ringing circuit employing gas-filled tubes that will operate in response to alternating currents alone without requiring the presence of direct currents also. In other words, it is the object of this invention to set up a ringing circuit which will operate the ringers when alterhating current alone of some predetermined frequency istransmitted over the line. Such an arrangement will eliminate direct current biases heretofore proposed for ringing circuits.

These and other objects of.this invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing in which Figure 1 illustrates one embodiment of the ringing circuit. arrangement ofthis invention given 55 merely. for the purposenof illustration and Fig- 2 illustrates the unbiased alternating current circuit used'to operate the apparatus of Fig. 1.".

Referring to-F'ig: l of the'dra'wingythe refer ence characters T and R represent twoiof the wires of a'telephoneiine'over which telephoned and'other signals may be transmitted." Across this line may be bridged a plurality of telephone. ringing circuits, fouriof whichare illustrated in the drawing by the letters A, B, and D.- The ringing circuitsAand B are similar to each 1 other and are connected between conductors T- and R in exactly the same manner.. The ringing circuits C and D are also alike and are con-, nected in reverse across the conductors T and R. Other similar ringing circuits may be connected across conductors -T andIRin either of the two ways shown in the drawing.

Each ringing circuit comprises a cold cathode gas-filled tube of well known-constructiomthe. varioustubes being designated G1, G2, G3 and 7 G4 in the various circuits, a res-istcr,. each..re-

sistor' being designated Z1, Z2, Z3 and Z4. in the respective circuits and a ringer labelled inthe various circuits W1, W2,..W3 and-W4, respec--v tively, as shown in-the-drawing.

The two cathodesof veach gas tube-are designated K1 and K3 andthese two electrodes :form thecontrol gap. of .the tube. Eaclitube also inn eludes ananode E. The maingap of each tube comprises the cathode K1 and .the anodeE.- I

It will be observed. that the cathodes Ki. oi tubes G1 and G2 are connected directly [tocon ductor T, thatresistors Z1 andZs. are connected between thecathodes Kz'ofthese same tubes and ground and-that the ringers W and W2 are connected between the respective anodes E .of' these tubes and the conductor-- R. Similarly, the cathodes Ki-of tubes G3 and G4 areconn'ected. directly to conductor R, the resistors ZaandHZiJ are connected between the cathodes Ka-Of the tubes G3 and G4, respectively, andground andf the ringers W3 and W4 are connected between the respective anodes E of the latter tubes and" the conductor T. v g

In order to'operate any of the ringers shown in the drawing, an alternatingv current (not shown in Fig. 1) is transmitted overthe conductors T and R, as will be explained herein after. Theringing current is alternating current alone, without any direct current bias componentwhatever.

we operate either or both of the ringers W1 and W2; one terminal of thealternating current sourceis connectedto the conductor 'T,' 'the other terminal: of: the; source: being grounded ande at the same time connected to the conductor R.

The voltage of this source is greater than that required to ionize the gas between the cathodes K1 and K2 of both tubes G1 and G2 and hence current will flow from the alternating current source over the control gaps K1--K2 of tubes G1 and G1 and over the respective resistors Z1 and Z2 in parallel to ground. Upon ionization of the gas of these tubes, the alternating current will then flow through both main gaps K1-E of the tubes G1 and G2 in parallel and through the respective ringers W1 and W2 and over conductor R which is grounded at the source. Both ringers W1 and W2 will then be operated. The subscribers having the ringing circuits A and B will be selectively signaled by predetermined 'codes in a well known manner sothat both subscribers will not answer the call intended for but one of the subscribers. These codes are formed, of course, by interruptions of the alternating current source. When the conductor R is grounded as, for example, during the time when ringers at stations A and B are operating, none of the ringing current will flow through the ringing circuits of stations C and D. It will be observed that during this period, the electrodes K1 of both tubes G3 and G4 are connected to ground by conductor R and that the electrodes K2 of these tubes are also connected to ground through resistors Z3 and Z4 and hence the gas Within the control gaps K1K2 of tubes G: and G4 remains deionized because no current flows therethrough. Furthermore the peak voltage of the alternating current ringing generator is less than the voltage required to ionize the gas between the main gaps K1E of both tubes G3 and G4 and hence no current will flow through ringers W3 and W4.

In one particular arrangement in which the circuit shown in the drawing was successfully operated, the various tubes were of the BIB-A type, the resistors such as Z1, etc., were of the order of 100,000 ohms and the alternating current generator was of a frequency of about 20 cycles and had an effective voltage which could be varied between '75 and 130 volts. The control gaps K1-Kz of the 3l3-A tubes will break down at around 70 volts, the main gaps K1-E will break down at 130 volts or at a somewhat higher voltage and, after the gas within the control gap K1K2 becomes ionized, the voltage required to transmit current through the main gaps K1E will be reduced to around '75 volts.

In order to transmit ringing current through the ringing circuits C and D, the ringing current generator is connected to conductor R and the conductor T is grounded at the: source. The gas within tubes G3 and G4 will become ionized and the current of the generator will flow through both ringers W3 and W4 in parallel. The subscribers having these respective ringers will be selectively rung by predetermined codes, in a manner well known in the, art. None of the current of the alternating current generator will flow through the tubes G1 and G2 and therefore the ringers W1 and W2 will remain unoperated.

An added feature of the circuit arrangement shown in the drawing is that it will not respond to interfering voltages emanating from electrified railways or the like. Any such voltage induced into either or both of the conductors T and R will ordinarily be impressed across the control electrodes K1K2 of each tube connected to the conductor or conductors exposed to the interfering voltage. Such a voltage may at times be large enough to ionize the gase within the tubes connected to the exposed conductor or conductors, but it will not be so large as to operate any of the ringers W1 to W4. The reason why such interfering voltages are unable to actuate the ringers is that each ringer-W1 to W4-is connected in series with the electrodes Kz-E of the corresponding tube and in series also with a large resistor-Z1 to Z4with respect to the interfering voltages and therefore any possible current flow through the ringers would be practically negligible.

Fig. 2 illustrates one form of circuit arrangement which may be utilized for operating any of the ringing circuits of Fig. 1. Here the generator of alternating current is designated M and it is connected to the conductors T and R through a potentiometer P and a double-pole doublethrow switch S. When the switch S is thrown to the right, one terminal of the generator M will be connected to the conductor T and its other terminal connected to conductor R which also becomes grounded. Ringing currents may then be transmitted to stations A and B of Fig. 1 to actuate the ringers W1 and W2, as already explained. When the switch S is thrown to the left, the position of generator M will be reversed with respect to conductors T and R and the ringers W3 and W4 of stations C and D may be actuated as already explained. The potentiometer P is employed to vary the voltage of generator M transmitted to conductors T and R whenever desired.

Any well known type of generator of alternating current suitable for operating the various ringing circuits may be used in place of the arrangement of Fig. 2, but it is essential that one terminal of the generator be grounded.

While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the invention may be set up in other and widely varied organizations without departing from the spirit of this invention and the scope of the appended claims.

What is claimed is:

1. A signaling arrangement operable by alternating current alone, comprising a pair of conductors, a three-electrode gas tube, a resistor connected in a series circuit with two of the electrodes of said tube and one of said conductors and ground, and a. ringer connected between the third electrode ofv the tube and the other conductor.

2. A ringing circuit comprising two conductors over which alternating current alone may be transmitted for ringing purposes, a three-electrode gas tube, one of the electrodes of said tube being directly connected to one of the conductors, a resistor connected between another of the electrodes of the tube and ground, and a ringer connected between the third electrode of the tube and the other conductor.

3. In a signaling system, a pair of conductors, two ringing circuits connected in reversed relation between said conductors, each ringing circuit comprising a three-electrode gas tube, a resistor and a ringer, one of the electrodes of each tube being connected to one of the conductors, another electrode being grounded through the corresponding resistor, the third electrode of each tube being connected to the other conductor through the corresponding ringer, a grounded generatorof alternating current, and means for connecting said grounded generator between said conductors in one direction or in the opposite direction. t-

4. A multi-party unbiased ringing system comprising first and second conductors,-first and second groups of ringing circuits connected in reversed relation between said conductors, each ringing circuit including a three-electrode 'gas tube, a resistor and a ringer, one electrode of each gas tube of the first group being connected to the first conductor, another electrode of each gas tube of the first group being connected to ground through the corresponding resistor, the third electrode of each tube of the first group being connected to the second conductor through the corresponding ringer; one of theelectrodes'of each tube of the second group being connected to the second conductor, another electrode of each tube of the second group being connected to ground through the corresponding resistor, the third electrode of each tube ofthe second group being connected to the first conductor through the. corresponding ringer.

5. An arrangement similar to that set forth in claim 4 including, in addition; a grounded alterr' 

